Synthesis and Reversible Transformation of Cu n -Bridged ( n = 1, 2, or 4) Silicodecatungstate Dimers

Three copper-bridged sandwich-type silicodecatungstate dimers, TBA(8)Cu(γ-SiW(10)O(34))(2)(CH(3)CONH)(2)·4H(2)O (Cu-1, TBA = tetra-n-butylammonium), TBA(8)H(4)Cu(2)(γ-SiW(10)O(36))(2)H(2)O·11H(2)O·CH(3)COCH(3) (Cu-2), and TBA(8)H(2)Cu(4)(γ-SiW(10)O(36))(2)(CH(3)COO)(2)·5H(2)O (Cu-4) have been selectively synthesized by reactions of divacant lacunary TBA(4)H(4)(γ-SiW(10)O(36)) (SiW10) with copper acetate in organic media. The copper cation(s) in Cu-1, Cu-2, and Cu-4 possess square-planar four-coordinate (Cu-1), square-pyramidal five-coordinate (Cu-2), and octahedral six-coordinate (Cu-4) geometries, respectively. These compounds can reversibly be transformed simply by controlling the copper/SiW10 molar ratios in solutions.